To determine the incidence, nature and subsequent management of complications occurring during right ventricular endomyocardial biopsy in patients with cardiomyopathy, all events occurring during 546 procedures in 464 consecutive patients were prospectively recorded. The internal jugular vein was the primary site of introduction in 96% of cases. A total of 33 complications (6%) occurred: 15 (2.7%) during catheter insertion including 12 arterial punctures (2%), 2 vasovagal reactions (0.4%) and 1 episode of prolonged bleeding (0.2%), all without sequelae; 18 (3.3%) during biopsy included 6 arrhythmias (1.1%), 5 conduction abnormalities (1%), 4 possible perforations (0.7%) and 3 definite perforations (0.5%) (pericardial fluid). Two (0.4%) of the three patients with a perforation died. There was no secular trend in the complication rate, nor were complications associated with specific clinical or hemodynamic characteristics. It is concluded that the overall rate of endomyocardial biopsy complications (6%) is low, but mortality may occur.